Thomas Harriot mapped the Moon before Galileo (J. Rampling Nature 508, 39–40; 2014). Unlike Galileo, he did not interpret what he saw as craters, mountains and valleys (see S. Pumfrey Notes Rec. R. Soc. 63, 163–168; 2009).

Galileo's experience in the visual arts gave him a theoretical background in mathematical perspective (see, for example, S. Y. Edgerton The Heritage of Giotto's Geometry 233–239, Cornell Univ. Press, 1991; and S. E. Booth and A. Van Helden Sci. Context 13, 463–486; 2000). This included using shadows to determine the volume and location of an object. Observing the Moon's surface with his perspicillum, later named telescope, Galileo's training as a draftsman led him to interpret variations in light on the surface as shadows produced by the Sun on a complex topography.

Harriot did not grasp the significance of these dark areas. He interpreted them simply as surface markings that he used to 'map' the Moon. Art and science have sometimes benefited each other in ways that we fail to appreciate.